This invention relates to an improvement in composite tape technology, more particularly to a machine and method for laying composite tape to form a laminated structural member. An aspect of the invention is a machine for compaction of the tail of a tape strip cut at a shallow angle, for example 60.degree. to 80.degree., from a line normal to the longitudinal axis of the tape. An aspect of the invention is a process of compacting a tape tail as aforesaid substantially all the way to the end of the tail. An aspect of the invention is to provide machine and process for compacting a tape tail which has been peeled away from the backing material.
Composite tapes and machines and methods for handling the same are described in a number of prior art publications. By composite tape, we refer to a strip of tectonic unidirectional filaments in a resinous matrix. The tape is removably adhered to a backing, usually a paper backing which can be peeled away. The tape is laid in parallel rows, one layer on top of another with adjacent layers usually laid in separate directions to create grain and cross grain features. Structures so made are polymerized i.e. the resinous matrix is cured in some fashion as by cross-linking, polymerizing, etc.) to form structural components, most commonly components of aircraft such as the horizontal and vertical stabilizer skins in lieu of the more conventional and older metallic skins, although automotive parts such as leaf springs are being made of composite material. The resin composition, filaments (which may be graphite, carbon, or in some case even glass) and matrices are well-known. Such structures--and for that matter the tapes--can be laid by hand, but the present invention is directed to a machine and process for laying the tape.
Prior art publications of interest here as representative of the state-of-the-art are U.S. Pat. No. 3,574,040 to Chitwood et al, U.S. Pat. No. 4,351,688 to Weiss et al, British Published application 2,101,519A to Murray et al, and U.S. Pat. No. 3,775,219 to Karlson and Hardesty.
The present invention is particularly concerned with compaction of the tail of an obliquely cut tape. Heretofore, compaction of such tails all the way to the end of the tape has presented a problem, especially on cut in excess of 60.degree. from a cut normal to the longitudinal tape axis (said normal cut being commonly called "straight across"). A long tail resulting from such a shallow cut presents a number of manufacturing and quality control problems. As one goes further along the tail towards its end, bearing pressure of the unused tapered tape tail itself (due to diminishing lateral size) may cause the unused length of tape to adhere more strongly to the mold and to the tail, thus creating delamination problems when the unused tape is removed. Experience has shown that the latter half of an elongated tail presents the worst problem because of the narrowing width.
Some of the prior art solutions to these problems have been to limit the angle of cut to some small amount, oftentimes 60.degree.; to limit the tape laying pressure to the first half of the tail and completing the compaction and trimming manually; and refraining from lay directions and laminated structures that would require a long tail.
The present invention has for an object provision of machine and method for compacting tape having a long tail substantially the full length of the tail regardless of how shallow or oblique the tail is cut. The present invention has for an object the provision of a method and machine for compacting tape by separating tape from the substrate or carrier on which it is usually carried and then applying compacting pressure only to the tail portion of the tape, thereby obviating many of the difficulties arising from having to separate the substrate or other support after compaction has taken place.
The present invention provides, among other things, a process of laying and compacting composite tape comprising the steps of cutting or severing the tape but not severing the support (such as backing paper release paper, etc.), separating the support and the tape, and applying the tape to a mold while storing the support material. The process preferably includes cutting the tape obliquely (thus forming a tail) before separating the support from the tail, being sure as before to not severe the support. Apparatus for laying composite material according to the invention includes means to separate the support material from the composite strip before compacting the strip against the mold, involving first and second compaction means, with the second such means being disposed between the support and tape at a location trailing the first compaction means which second means is located to apply compacting pressure to the tape--usually the tail--only and means to position the respective compaction means for compacting at different times.
An important feature of the process and of the compaction apparatus is separating the support from the tape before compacting the tail. A machine according to the invention provides means to do this. The machine and process of this invention each contemplate cutting or severing the tape but not severing the backing paper (i.e. substrate, or other support) on which the tape comes mounted. Both the machine and process also contemplate switching from a compaction means that applies pressure to the assembly of backing and tape to a means that applies pressure only to the tail after the backing and tail portion of the tape have been separated.